The present invention is directed to relatively small sized rechargeable batteries used as a power source for mobile electronic devices such as mobile phones or mobile personal computers and wireless equipment such as cordless phones, e.g., a nickel-metal hydride rechargeable battery, a nickel-cadmium rechargeable battery, and so on.
Nickel-metal hydride rechargeable batteries satisfy all the three requirements for the battery power source of mobile or electric equipment: High capacity, high energy density, and good cost performance. Because of the low electromotive force (nominal voltage: 1.2V), however, one cell can hardly supply a voltage required for operating the equipment, and so in most cases a plurality of cells are connected in series to provide the required output voltage. Most commonly, the cells are series-connected and constructed as a battery pack.
A battery pack consists of several series- or series-parallel-connected cells packed with a heat shrinkable tube or the like to be united as one body. FIG. 8 shows the widely known structure of one such battery pack: Four cylindrical cells 30 are connected in series with connecting plates 32; a thermal protector 33 is interposed in the series circuit; positive and negative terminals 34 and 35 are respectively attached to the cells 30 at either end such as to extend to the outside; and the cells are entirely packed with a heat shrinkable tube 31.
Japanese Patent Laid-Open Publication No. Hei 13-126690 shows another type of battery pack: A plurality of (three in the example) series-connected prismatic cells 200 are accommodated in a frame body 101, as shown in FIG. 9.
Further, Japanese Patent Laid-Open Publication No. 2001-57199 shows a battery module for constructing a rechargeable battery pack suited for high power applications such as electric or hybrid electric/gasoline vehicles. A plurality of (six in the example) cell cases 53 that each accommodate elements for electromotive force are united as one-piece battery case 52 to form a battery module from a plurality of rechargeable batteries, as shown in FIG. 10. In this battery module, the plurality of rechargeable batteries are coupled together such that each two adjacent cell cases 53 share the end wall between them, and that the elements for electromotive force in each cell are connected in series. Several such battery modules are further coupled side by side, and the side walls of the battery case have numerous bosses and ribs that will form air passages for effective heat dissipation between adjacent battery modules. The upper open end of the united battery case 52 is closed by a lid 54. The inside of the battery case 52 is divided by partitions or the end walls of the cell cases 53. Suitable connection means are provided to connect the elements for electromotive force of adjacent cells in series. The cells at either end are connected to input/output terminals 55 attached at both ends of the battery case.
Batteries that generate low electromotive force as one cell such as nickel-metal hydride batteries have conventionally been constructed as a battery pack or module as described above so as to provide the voltage that the equipment requires to operate. Battery packs necessitate various constituent elements other than the cells themselves and tend to have increased costs and volumes.
In the structures shown in FIG. 8 and FIG. 9 where a plurality of cells are connected in series, adjacent cells are oriented upside down so that the cells are readily connected in series. Some cells are therefore always inverted, with their sealing parts facing down. Since there is some space in the sealing part between the electrode plate assembly and sealing plate, it is possible that liquid electrolyte leaks into this space if the cells stand upside down for long time.
What is worse, battery packs that use pack cases or heat shrinkable tubes as means of binding a plurality of cells are low in mechanical strength and necessitate a reinforcement especially when used for mobile devices or electric tools.
An object of the present invention is to provide a novel structure that enables an alkaline rechargeable battery, which as one cell has low electromotive force, to have a higher output voltage applicable to various equipment, without resorting to common battery pack structures.